Electrical resistor



, Z'nvenor fle/15T Hgo/65,42 Wam-e E. fcH/afmufe Hor ey E. HEDGER ETAL ELECTRICAL RESISTOR Filed Sept. 24, 1942 Sept. 25, 1945.

Patented Sept. 25, 1945 ELECTRICAL RESISTOR Ernst Hediger and Walter E. Schildhaner, Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application September 24, 1942, Serial No.459,514

16 Claims.

This invention relates to electrical resistance elements. Electrical resistance elements comprehended within the present invention are useful in many dillerent applications. Because of their resistance to deterioration at high temperatures, they are particularly useful where high temperatures ara encountered during their operation. 'I'hey are also stable in ohmage values at ambient elevated temperatures, thus making unnecessary any provision for compensating for changes in resistance of the resistor with its length of service.

'I'he resistor of the present invention, although not limited to such use, is particularly advantageous in applications where fairly high resistance is required and the space available for the resistor is limited. Wire wound resistors are large because of the ohmage values required, which may be, in the case of the starting resistor for mercury arc lamps, between 20,000 and 50,000 ohms. To attain such ohmage values in a wire wound resistor small enough to fit into the limited space available, the wire used must be very small in diameter and the insulation light. Because of such inherent limitations in design, wire wound resistors of this type frequently develop open circuits or short circuits.

Composition resistors have been employed for such purpose, but those used before the present invention have not performed satisfactorily because they changed in resistance value as their length of service increased. Furthermore, because of the high temperature at which they were operated, theyA tended to burn out and thus open circuit after a relatively short period of use.

The present invention overcomes the above difficulties and others encountered with the use of wire wound resistors and the prior art composition resistors where they are operated at high temperatures for long periods of tme `or encounter still higher temperatures for short periods of time. The invention will be more readily understood by reference to the accompanying drawing, which is for purpose of illustration only, in which Fig. 1 is a view in cross-section of a resistor element embodying one form of the invention,

Fig. 2 is a view in cross-section of` a modification of the resistor of the present invention,

Fig. 3 is a view in cross-section of another modillcation of the resistor,

Fig. 4 is a cross-sectional view of an apparatus employed in the making of the resistor shown in Fig. 3, and

herent mass.

Fig. 5 shows, in cross-section, a mercury arc lamp in which the resistor may be employed.

The resistance element shown in Fig. 1 is made up of a resistance member denoted generally by the reference character I, which. consists of a resistance core member 2 composedof an electrical conducting material such as carbon distributed in a vitrifled insulating matrix, and a rigid ceramic jacket 3 surrounding the core and vitrified into an integral mass Withthe core, y No novelty is claimed for the resistance member I per se. Such resistance member and its method of manufacture are disclosed and claimed in U. S., Patent No. 2,060,393, issued November 10, 1936, to A. H. Heyroth. Briefly, such member I is made by forming a mix containing carbon, a clay binder, and a filler of poor electrical conductivity in comparison with carbon, such as silicon carbide, ilint, or Zircon. The mix is moistened with suilicient water to impart plasticity thereto and is then extruded or otherwise formed into rods, or other desired shapes, and dried. The formed shapes are then given an oxidation treatment by heating at 900 F. or over in an oxidizing atmosphere .to oxidize the conducting material in the outer portions thereof, after which they are hardened by firing at a higher temperature to effect at least a partial vitriiication of the clay binder or a sintering of the resistor into a strong co- A length of such product is then cut of! sumcient to form member I, or if individual resistor members were formed, the ends are cut oil to expose the conducting core 2 at the ends of the resistor member I.

Electrical connection is made with the con- 'ducting core 2 by metal spraying the ends of .member I with a coating l of nickel or iron or other suitable metal, such coating extending down the sides of the member for a substantial distance, as shown in Fig. 1. Over this coating l at each end of the resistor member i is forced a metal cap 5 equipped with lead wires 6. In one instance the caps 5 are made of nickel or iron and the lead wires B are composed of iron or of Monel metal, an alloy composed of 60 parts nickel and 40 parts copper. It is obvious that caps and 'lead wires made of different metals may be emlplayed if desired.

For the purpose of sealing the resistance from lthe atmosphere and thus making it capable of operation at fairly elevated temperatures without damaging the resistor core or altering its electrical characteristics by reason of oxidation of' the conducting core, the member I is coated, in accordance with the present invention, with a glaze 'I which extendsover the edges of the caps as shown. To enable the glaze to maintain an airtight seal with caps and shell 3, it must possess a coeicient of thermal expansion substantially the same as that of caps 5 in the range between room temperature and the highest temperature under which the resistor operates or to which it is subjected in installation. Various glazes which meet this requirement may be' ernployed for coating 1. As an example, a glaze having the following composition has been found highly satisfactory where caps 5 are made of nickel or iron:

It is to be understood that this glaze is illustrative only, and that it is capable of variation, and -that other glazes may be used instead of it. The glaze mixed with water to form a paste or slurry is coated on to the resistor element I and over the ends of caps 5. The resistor is heated at ISO-250 F. until the glaze is dried, and is then red for from 1 to 2 minutes at from 1400 to 1700 F. -to cause the glaze to melt and flow. When cool the glaze seals the caps to the resistor member and seals the resistor member itself, making them impervious to the atmosphere, and preventing oxidation of the resistance material and the end contacts.

The resistor shown in Fig. 1 is useful where moderately high temperatures are encountered in service. Because it is sealed it also has a long life when used at ordinary temperatures, the resistance core I retaining its initial resistance despite long usage, as it is unaiected by atmospheric conditions.

Where the resistor must operate under high temperature conditions or must be subjected to high temperatures during its installation in operating position in a device in which it is to be used, as for instance, in lamps such as mercury arc lamps, it is preferred to use a resistor still further sealed and protected. Such resistor is shown in one modification in Fig. 2 and in another modification in Fig. 3.

The resistor shown in Fig. 2 consists essentially of the element shown in Fig. 1 with a further outer ceramic shell around it and a second glaze on said outer ceramic shell. It is made by assembling the resistor element I with wet unflred glaze coating I thereon into the prered ceramic tube 8, which in one example is of substantially the same composition as the outer layer 3 of the resistor member. The open ends of tube 8 are then plugged with plugs 9 of a suitable material, for example a vitriable material. One such substance is a mixture of 80% of the same composition as tube. 8 and 20% of a frit of the following composition:

Per cent NazO 3.68 CaO 4.41 PbO 30.46 B203 12.60 A1203 3.41 S102--- 42.82 ZrOa 2.30

It is obvious that such plugging material may be varied in composition and that other mixtures may be employed.

'I'he resistor is then heated at 19o-250 F. to

Parts by weight Jasper ini' 4 Bentonite clay 4 Zirconium oxide 8 and 80 parts by weight of a frlt which is composed of Per cent NaaO 3.68 .Can 4 41 PbO-- 30.46 B201 12.60

` Al2O3 3.41 S102 42.82 2.30

" ZrOz The outer or over glaze coating is dried by heating the resistor to a moderate temperature, for instance 190-250 F., after which the resistor is fired for from 1 to 2 minutes at from 1700 to 2000 F. to melt the glaze and cause it to ow completely and uniformly around the resistor as shown at I0.

Ceramic tube 8, plugs 9, and over glaze I0 prevent oxidation of the body of the resistor and prevent the under glaze I from gassing when the resistor becomes highly heated as an incident to its operation at high temperatures or its being assembled into a lamp or other device.

In the modication of -the resistor shown in Fig. 3 the outer protective jacket II is applied by molding a suitable mixture around the resistor member shown in Fig. 1 and then ring to vitrify it. An over-glaze I2 is then applied over the jacket in the same manner as described in connection with Fig. 2. The molding of the jacket may be done in a variety of ways, as well as by hand. The apparatus shown in Fig.. 4 has been found convenient for accomplishing such molding. This apparatus consists of a die block I3 of metal having a bore I4 therethrough of the desired size of the resistor jacket. Two plugs or pistons I5 which closely fit the bore I4 are provided, one for each end of the bore. These pistons have small coaxial bores I 6 through them to receive the lead wires 6 from the resistance element I.

In-operation, one piston I5 is placed in bore I4, and the die block positioned vertically, with piston I5 resting on the bottom support I8 of a power press. A member I9, which is U shaped in cross section to allow its removal by being moved laterally, is placed under die I3 to support it temporarily. A measured quantity of the mixture to form the outer jacket, which may be of the same composition as used for plugs 9 in the modification shown in Fig. 2, is placed in the die lbore I4 and evenly distributed on the assembled b'ottom piston I5. A resistor element I is then placed coaxially in the bore with the bottom lead Wire 6 extending into bore I6. A measured quantity of the same mixture to form the jacket is poured around the resistor and on top of it. The second piston I5 is then assembled in the die bore I4 with lead wire 6 extending into bore I6. Top

y piston I5 is pressed downwardly by press plunger 2,385,702 nal molding pressure on the resistor. The relamp, such as illustrated, after becoming highly sistor is ejected by moving bottom piston I6 over heated as from operation for a considerable an opening in the press bed or support I8, large period of time is shut oi for any reason such as enough to allow the jacketed resistor to pass power failure for even a fraction o! a cycle, it through it supporting die I 4 by support I9, and 5 will not again function to establish an arc bepressing the resistor out by force exerted on the tween electrodes 22 and 23 until the lamp has top piston i6.' cooled down so that pressure within sheath 26 After packet ILhas been tired, over-glaze I2 becomes materially lowered, which may take as is applied to the resistor and ilred, as described long as five or ten minutes. If power is re-esin connection with the application of the over 10 tablished during this period, the starting arc then glaze to the resistor in Fig. 2. is created and maintained between starting elec- As has been previously explained, the mounting of resistors in certain typ their exposure to high te in the case of mercur trode 2| and main electrode 22. This causes resistor 20 to carry a, considerable current for a substantial length of time. When a mercury arc light source of the type shown in Fig. is employed in certain ultra violet lamps, the outer glass sheath is made of glass which passes only .ultra violet light. Such sheath absorbs or reflects all radiant energy from the arc except the 2o ultra violet, and thus the interior of the outeres of apparatus entails mperatures. This is true y arc lamps of the type l5 illustrated in Fig. 5, in which the arc starting mechanism employs a series resistance located near the base of the lamp. This resistance, shown at 20 in Fig. 5, is connected in series withv the starting arc between starting electrode 2| and the bottom main electrode 22 when the lamp is conource of electric current. he tube becomes sulciently p and found zing atmostest involvmmmmmmmwwwnw gs. 2 and 3 withd operation condicooling resist- 3. The resistors umace at 1300 F.,

ycle, and change after each cycle tors numbered 1 y constant throughp, since it is completely ph ere and other gases ly aiIect it.

y of resistance value e, and left for minut, allowed to cool, and mined. The resistors ven such heating and of the test the average he twelve resistors was mwawtmmmmwammmm..

y the resistor becomes very able-free service. The represent invention under hi ons in an oxidi mmmommmmmmmm mmmmmmmmmmm.

They were taken o In the following table the original resheath and consequentl hot.

Resistor thus is subjected to very severe treatment during its installation in the 1am ring operation of the lamp. It has been that resistors such as shown in Fi stand this severe installation an tions, and yield long tro sistance remains substantial! sealed from the atmo which might deleterious The remarkable constanc of the resistor of the phere is shown by the results of a ing repeated cycles of heating e; ors such as shown in Figs. 2 and were put into an electrical f with air as the atmospher utes. their resistance value deter were subjected in all to se cooling cycles. At the end 10.8%. sistanoe, resistance vafter each c in resistance from the original is given for each of twelve resis '11,() out the life of the lam change in resistance of t to l2.

uch less is and and the startsheath inguished and no is assembled by ort wires in the press sheath 25. This the outer glass 35 temperature conditi point 21. Press 24 has r to unite the 26 to part 28 the botowomamownmuwcoycmomamom 111111111111 an arc is established bed 23, which are connected 25 du arting electrodes. Because main arc is now rn ojecting from the eleche top of part 28 are 4U 29 while being suitably tion. When sufficiently n slightly at the bottom n the part 28 is pressed sheath 26 a sealed joint re- LLLLLLLLQU..L.LL

Repeated temperature test of resistors, heating to 1300 F. for 10 min. and cooling ammmammmmmmm The lamp shown in Fig. 5 welding the lead and supp 24 to the lead wires pr This heating of the outer glass sheath for the nected to a suitable s When the mercury in t vaporized and ionized tween electrodes 22 an in parallel with the st the resistance of the than that through resistance 20 ing arc, the starting arc is extin current flows through the starting circuit.

trodes in the inner sealed glass assembly is then slipped into sheath which terminates at the bottom portion 28 of the outer tegrallyl connected to it. In ord bottom portion oi' sheath tom of sheath 26 and t heated as by gasames turned in a vertical posi heated the glass necks i of sheath 26 and whe against the bottom of sults. A conventional lamp ibase, not shown connected to the lamp lead wires 30 and 3| cemented to part 28 of the outer glass sheath to complete the lamp.

This test demonstrates, besides the substantial ancy of electrical resistance of such resistors, their ability to withstand heat shock, since as above pointed out, each cycle involved the Furthermore, durplacing of cold resistors directly into a furnace emperature inside 'at 1300 F., with no preliminary warming up.

While the resistor has been illustrated and depurpose of sealing it subjects the mechanism inside it, including resistor 20, which is about opconst pcsite the zone of maximum temperature of the sealing flames to intense heat, in the order of 1300 F., for several minutes.

ing normal operation the t sheath 26 rises to about 600 F. When a mercury 75 scribed speciiically in connection with a mercury arc lamp, it is obvious that it is useful in other types of lamps such assodium arc lamps and neon lamps. Furthermore, the resistor is useful in all applications where high temperatures are encountered in its installation or operation, and/or atmospheres are encountered at normal temperatures which without the fully sealed construction of the resistor would destroy it or substantially change its resistance value.

It is therefore to be understood that the details herein described with respect to the resistor may be variously changed and modified without departing from the spirit and scope of the invention except as pointed out in the annexed claims.

We claim as our invention:

1. An electrical resistor comprising a resistance core of electrical conducting material in a rigid jacket surrounding the core, metal caps on the ends of the resistor making electrical connection with the resistance core, and a vitrified glaze on the outside of the jacket adjacent the caps and extending over the inner ends of the caps and making an air-tight joint with the caps, said glaze being of substantially the same thermal coeihcient of expansion as the metal caps.

2. An electrical resistor comprising a resistance core of electrical conducting material in a rigid ceramic jacket surrounding the core, metal caps on the ends of the resistor making electrical connection with the resistance core, and a continuous vitried glaze on the outside of said jacket and overlying the inner ends of the caps and making an air-tight joint with the caps, said glaze being of substantially the same thermal coeilicient of expansion as the metal caps.

3. An electrical resistor comprising a resistance core of electrical conducting material distributed in a vitriled insulating matrix, a rigid ceramic jacket surrounding the core and vitriiled into an integral mass with saidv core, metal caps on the ends of the resistor making electrical connection with the resistance core, and a continuous vitriiied glaze on the outside of said jacket and overlying the inner ends of the caps and making an air-tight joint with the caps, said glaze being of substantially the same thermal coefcient of expansion as the metal caps.

4. An electrical resistor comprising a resistor core of electrical conducting material in a rigid jacket surrounding the core, metal caps equipped with lead wires on the ends of the resistor making electrical connection with the resistance core, a vitrified glaze on the outside of the jacket adjacent the caps and extending over the ends of the caps, said glaze being of substantially the same thermal coeiiicient of expansion as the metal caps, an outer sheath of ceramic material enclosing the jacketed resistor core, the cap lead wires extending through such outer sheath, and a vitried glaze covering the outer sheath and sealing it from the atmosphere.

5. An electrical resistor comprising a resistance core of electrically conducting material in a rigid ceramic jacket surrounding the core, metal caps equipped with lead wires on the ends of the resistor making electrical connection with the resistance core, a continuous vitriiied glaze on the outside of said jacket and overlying the ends of the caps, said glaze being of substantially the same thermal coeilicient of expansion as the metal caps, an outer sheath of ceramic material enclosing the jacketed resistor core, said sheath comprising a prered ceramic tube fitted over the resistor and ceramic plugs lling the ends of the tube, the lead wires extending through the outer sheath, and a vitriiled glaze covering the outer sheath and sealing it from the atmosphere.

6. An electrical resistor comprising a resistance core of electrically conducting material in a rigid ceramic jacket surrounding the core, metal caps equipped with lead wires on the ends of the resistor making electrical connection with the resistance core, a vitriiied glaze on the outside of the jacket adjacent the ends of the caps and extending over the ends of the caps, said glaze being of substantially the same coeilcient of expansion as the metal caps, an outer sheath of ceramic material molded around and enclosing the jacketed resistor core, the cap lead wires extending through such outer sheath, and a vitriiled glaze covering the outer sheath and sealing it from the atmosphere.

7. An electrical resistor comprising a resistance core, high temperature resistant insulating material on the core, metal caps equipped with lead wires on the ends of the resistor making electrical connection with the resistance core, a vitried glaze on the outside of the jacket adjacent the ends of the caps and extending over the ends of the caps, said glaze being of substantially the same coeiiicient of expansion as the metal caps, an outer sheath of ceramic material enclosing the insulated resistor, the lead wires extending through the outer sheath, and a vitried glaze covering the outer sheath and sealing it from the atmosphere.

8. An electrical resistor comprising a resistance core of electrical conducting material in a jacket surrounding the core, metal caps on the ends of the resistor making electrical connection with the resistance core, and a vitried glaze on the outside of the jacket adjacent the caps and extending over the inner ends of the caps and making an air-tight joint with the caps, said glaze being of substantially the same thermal coefcient of expansion as the metal caps.

9. An electrical resistor comprising a resistance core of electrically conducting material, a jacket surrounding the core, means at the ends of the resistor making electrical connection with the resistance core, and a vitried glaze on the outside of the jacket adjacent the electrical connector means extending into intimate contact With the connector means and making an airtight joint therewith, the said glaze being of substantially the same thermal coeiicient of expansion as the electrical connector means.

10. An electrical resistor comprising a resistance core of electrically conducting material, a jacket surrounding the core, metal electrical connector means at the ends of the resistor making electrical connection with the resistance core, and a vitried glaze on the outside of the jacket adjacent the electrical connector means extending into intimate contact with said connector means and making an air-tight joint therewith, said glaze being of substantially the same thermal coeillcient of expansion as the electrical connector means.

11. An electrical resistor comprising a resistance core of electrically conducting material, a rigid jacket surrounding the core, metal electrical connector means at the ends of the resistor making electrical connection with the resistance core, and a vitried glaze on the outside of the jacket extending into intimate contact with the electrical connection means and making an air-tight joint therewith, said glaze being of substantially the same thermal coeilicient of expansion as the metal electrical connector means.

i12. An electrical resistor comprising a resistor core of electrical conducting material in a jacket surrounding the core, electrical connector means equipped with electrically conducting leads at the ends of the resistor making electrical connection to the resistance core, a vitried glaze on the outside of the jacket adjacent the electrical connector means extending into intimate contact with the connector means and making an airtight joint therewith, said glaze being of substantially the same thermal coeilicient of expansion as the electrical connector means, an outer sheath of ceramic material enclosing the jacket resistor core, the electrically conducting leads extending through such outer sheath, and a vitriied glaze covering the outer sheath and sealing it from the atmosphere.

13. An electrical resistor comprising a resistor core of electrically conducting material in a jacket surrounding the core, electrical connector means equipped with electrically conducting leads at the ends of the resistor making electrical connection with the resistance core, a continuous vitried glaze on the outside of said jacket extending into intimate contact with the electrical connector means and making an air-tight joint therewith, said glaze being of substantially the same thermal coeilicient of expansion as the electrical connector means, an outer sheath of ceramic material enclosing the jacketed resistor core, said sheath comprising a, preiired ceramic tube tted over the resistor and ceramic plugs lling the ends of the tube, the electrically conducting leads extending through the outer sheath, and a vitriiled glaze covering the outer sheath and sealing it from the atmosphere.

14. An electrical resistor comprising a resistor core of an electrically conducting material in a jacket surrounding the core, electrical connector means equipped with electrically conducting leads at the ends of the resistor making electrical connection with the resistance core, a vitried glaze on the outside of the jacket extending into intimate contact with the connector means and making an air-tight joint therewith, said glaze being of substantially the same coeflcient of ex pansion as the electrical connector means, and an outer sheath of ceramic material molded around and enclosing the jacketed resistance core, the electrically conducting leads extending through such outer sheath, and a vitried glaze covering the outer sheath and sealing it from the atmosphere.

15. An electrical resistor comprising a central resistance core of electrically conducting ceramic material, a jacket surrounding the core, means at the end of the resistor making electrical connection with the resistance core, and a vitried glaze on the outside of the jacket adjacent the electrical connector means extending into intimate contact with the connector means and making an air-tight joint therewith, said glaze having substantially the same thermal coeilicient of expansion as that of the electrical connector means.

16. An electrical resistor comprising a, rigid central resistance core of electrically conducting vitried ceramic material, a rigid ceramic jacket surrounding the core, means at the end of the resistor making electrical connection to the resistance core, and a vitried glaze on the outside of the jacket and adjacent the` electrical connector means and extending into intimate contact with the connector means and making an airtight joint therewith, the said glaze having substantially the same thermal coeilicient of expansion as that of the electrical connector means.

ERNST HEDIGER. WALTER E. SCIIUJDHAUER. 

